Accession No

2089

Brief Description

‘Simplon’ slide rule, English, 20th C

Origin

England

Maker

Simplon

Class

calculating

Earliest Date

1900

Latest Date

1970

Inscription Date

Material

wood; plastic (ivorine, perspex); paper (card and one other); metal (white metal)

Dimensions

case length 340mm; breadth 55mm; thickness 20mm

Special Collection

Provenance

Donated private individual, England, 28/8/1975.

Inscription

‘“SIMPLON” PRIMARY
(LOG-LOG) SLIDE RULE
(PATENT NO 413308)
MADE IN ENGLAND’ (obverse of rule)
‘J. B. Homer.
88, Stretton Road,
73 WESTCOTES DRIVE
Leicester.’ (case)

Description Notes

Wooden slide rule faced with ivorine; perspex cursor with white metal spring.
Upper part of stock carries scale marked ‘LU’, divided 1.1 - 3.2, numbered 1.1, 1.12...1.2, 1.25...1.8, 1.9...3, 3.2. Also scale marked ‘A’, divided [0.79] - [128], numbered [0.]8, [0.]9, 1, 2, 3, π, 4, 5...10, 20, 30, M, 40, 50...100.
Slide has indentical scale to ‘A’, but marked ‘B’. Two further scales marked ‘C’ with one being the inverse of the other, each divided [0.89] - [11.2], numbered [0.]9, 1...2, 3...1[0], [1]1. Lower part of stock carries scale marked ‘D’ which is identical to second ‘C’ scale. Also scale marked ‘LL’, divided 2[.]5 - 105, numbered 2[.]5, 2[.]6...3, 3[.]5...6, 7...10, 15...30, 40, 50, 100, 2[00]...103, 2[000]...5[000], 104, 2[0000]...5[0000], 105.
Card slip case embossed with name and address of original owner.
Reverse has tables of conversion factors and formulae.

Condition good; complete.

References

Events

Description
Developed during the seventeenth century, the modern slide rule is based upon the design by William Oughtred (circa 1630). It is one of many calculation devices that is based on the logarithmic scale, a calculation method invented in 1614 by John Napier.

Before the rise of the pocket electronic calculator in the 1970s, the slide rule was the most common tool for calculation used in science and engineering. It was used for multiplication and division, and in some cases also for ‘scientific’ functions like trigonometry, roots and logs, but not usually for addition and subtraction.

A logarithm transforms the operations of multiplication and division to addition and subtraction according to the rules log(xy) = log(x) + log(y) and log(x/y) = log(x) - log(y). The slide rule places movable logarithmic scales side by side so that the logarithms of two numbers can be easily added or subtracted from one another. This much simplifies the alternative process of looking up logs in a table, thus greatly simplifying otherwise challenging multiplications and divisions. To multiply, for example, you place the start of the second scale at the log of the first number you are multiplying, then find the log of the second number you are multiplying on the second scale, and see what number it is next to on the first scale.

FM:42510